If you are looking for the movie of the same name, please see Airplane!.

An aircraft is any machine capable of atmospheric flight.
Aircraft fall into two broad categories:

Heavier than air aerodynes, including autogyros, helicopters and variants, and conventional fixed-wing aircraft: aeroplanes in international English, airplanes in American English. Fixed-wing aircraft generally use a propeller or jet engine to provide thrust, which moves the craft forward through the air. The movement of air over the wings produces lift, which allows the aircraft to fly. Exceptions are gliders which have no engines and gain their thrust from gravity. That is, in order to maintain their forward speed they must descend in relation to the air (but not necessarily in relation to to the ground). Helicopters and autogyros use a spinning rotor (a rotary wing) to provide both lift and thrust. The abbreviation VTOL is applied to aircraft other than helicopters that can take off or land vertically. Similarly, STOL stands for Short Take Off and Landing.

Lighter than air aerostats: balloons and airships. Aerostats float in air in the same way that a ship floats in water, by displacing the air around the craft with a lighter gas (helium or hydrogen), or hot air. The distinction between a balloon and an airship is that an airship has some means of controlling forward motion and steering while balloons simply drift with the wind.

A first division by design among aircraft is between lighter-than-air and heavier-than-air aircraft.

Examples of lighter-than-air aircraft include non-steerable balloons, such as hot air balloons and gas balloons[?], and airships (sometimes called dirigible balloons), such as blimps (which have a non-rigid construction) and rigid airships, which have a rigid frame.
The best-known type of rigid airship is the Zeppelin.

In heavier-than-air aircraft, we can discern two major ways to produce the lift: aerodynamic lift and engine lift.
In the case of aerodynamic lift, the aircraft is kept in the air because of aerodynamics, usually by means of wings of some kind.
With engine lift, the aircraft defeats gravity by sheer engine power.

Among aerodynamically lifted aircraft, the largest number falls in the category of fixed wing aircraft, where horizontal surfaces produce lift, usually by profiting from Bernoulli's principle (aeroplane or airplane).

In a "conventional" configuration, the lift surfaces are placed in front of a control surface or tailplane.
The number of lift surfaces varied greatly in the pre-1950 period, as biplanes (two wings) and triplanes[?] (three wings) were numerous in the early days of aviation. Subsequently most planes are monoplanes.

The reverse configuration is the canard type, where small horizontal control surfaces are placed towards the nose of the aircraft ahead of the lift surfaces.

Other possibilities include the delta-wing, where lift and horizontal control surfaces are combined, and the flying wing, where there is no separate vertical control surface (e.g. the B-2).
A variable geometry ('swing-wings') has also been employed in a few examples of combat aircraft (the F-111, Panavia Tornado, and B-1 Lancer, among others).

The lifting body configuration where the body itself produce lift has been tested.
So far the only significant practical application of the lifting body was in the Space Shuttle.

A further category might encompass the wing-in-ground-effect types, for example the Russian ekranoplan, also nicknamed the "Caspian Sea Monster" and hovercraft, most of the latter employing a skirt and achieving limited ground or water clearance to reduce friction and achieve speeds above those achieved by boats of similar weight.

Some types of aircraft, such as the balloon or glider do not have any propulsion. Balloons drift with the wind.
For gliders, take-off takes place from a high location, or the aircraft is pulled into the air by a ground-based winch or vehicle or towed aloft by a powered "tug" aircraft.

Most early aircraft used a piston-engine with propeller as propulsion.
Although the configuration of the engine can vary (rotary, radial, inline), they all work according to the same principles.

Three major uses for aircraft may be seen: recreational, military and commercial.

For recreation, almost any type of aircraft can be used, although they are usually small ones.
Gliders and balloons are used almost exclusively for recreational purposes although they have been used in times of war in the past.
For instance, balloons were used for observation in the American Civil War and World War I.
Gliders were used to deliver troops into occupied territory during World War II.

The first widespread use of military aircraft was for reconnaissance and surveillance in World War I.
Soon they were adapted for attacking the ground or enemy vehicles/ships/guns/aircraft as well, and the first bombers were born.
In order to prevent the enemy from bombing, fighter aircraft were developed to intercept and shoot down enemy aircraft.

Eventually two seater trainers were developed for the purpose of instructing new pilots.
The use of transport aircraft enabled the rapid movement of supplies, ammunition, cargo, troops and also casualty evacuation; transport aircraft were also used to drop paratroopers.
Tankers are used to refuel planes in mid-air, thus increasing their operational range.

Commercial aviation can be divided in passenger transport and cargo transport.
For the former, large planes have been developed that can transport up to 500 passengers over large distances.
Commercial cargo aircraft are often similar to military transport aircraft, or might be adapted from the passenger fleets of an earlier era.

Other uses include search and rescue operations (especially by helicopters), border protection and water-bombing (fire-fighting).

Further divisions can be drawn between aircraft designs having a conventional (wheeled) undercarriage, and amphibious float-planes[?] or flying-boats[?].